The invention relates to tool holders in general, and more particularly to improvements in holders for rotary tools which can be used in automatic machine tools, such as drilling, boring, grinding, milling and/or other machines. Still more particularly, the invention relates to improvements in tool holders of the type wherein a housing supports a rotary spindle or shaft for one end portion of a rotary material removing or like tool, e.g., a grinding wheel.
It is already known to install a two-part spindle for a rotary material removing tool in a composite (multiple-section) housing. The two parts of the spindle are connectable to each other by a quick-release coupling, and the sections of the housing are also separable from each other so that the section which supports the tool-carrying portion of the spindle can be detached from another section. This renders it possible to inspect the tool, to replace the tool with a fresh tool, or to replace the detachable section with or without a tool on the respective part of the spindle.
A machine which is designed to treat complex workpieces must be equipped or furnished with a number of different tools which are needed to carry out different operations on a particular workpiece or to carry out different operations upon successively treated workpieces. This also applies for numerically controlled machines wherein the treatment is automated, either fully or to a large extent, in order to increase the output and to reduce the likelihood of unsatisfactory treatment due to human errors. In other words, even the operation of a fully automated machine tool or another machine must be interrupted for a relatively long interval of time if a previously used tool is to be replaced with a fresh tool or with a different tool.
Attempts to avoid lengthy interruptions of operation of fully automated machines involve the transfer of workpieces from machine to machine so that each machine can operate with a particular tool or a particular set of tools. Thus, such proposal renders it possible to avoid frequent replacement of tools in a particular machine but it exhibits the drawback that valuable time is lost for transfer of workpieces from machine to machine. Moreover, each transfer of a workpiece from a preceding machine into a following machine involves the risk of inaccurate positioning of the workpiece with reference to the material removing and/or other work treating instrumentalities. Therefore, such production lines must be equipped with complex and expensive monitoring devices which ascertain the position of a workpiece in each machine and with complex, expensive and sensitive means for adjusting the position of the workpiece prior to treatment.
It was further proposed to provide a holder for tools which are provided with hollow conical mandrels. The mandrel of a tool which is to be affixed to the holder confronts the holder and has an internal recess or groove for portions of clamping tongs which serve to draw the mandrel into the holder. The tongs can act upon a package of dished springs through the medium of a rod. The springs bias the tool to its operative position relative to the holder, and their bias can be assisted by a system of wedges. The means for disengaging the tool from such holder includes a piston which is reciprocable in a hydraulic cylinder and can be moved to a position in which it compresses the package of springs and disengages the system of wedges to thereupon open the tongs through the medium of the aforementioned rod. The tool is released and can be expelled from the holder in response to forward movement of the rod and the resulting opening of the tongs.
The tongs, the rod, the package of dished springs and the system of wedges rotate with the tool and with the hydraulic cylinder. This exhibits the advantage that the relatively long and sleek mandrel of the tool can be readily separated from the holder in spite of the need for the establishment of a pronounced retaining force when the tool is in use and is driven at a very high speed. Moreover, the just discussed holder can rotate without overly stressing the bearings for its rotary parts. However, the combined mass of all rotary parts is very high which is undesirable if the tool is to be rapidly accelerated or decelerated.
Commonly owned German Pat. No. 33 34 001 discloses a holder for grinding tools wherein the tool carrying spindle rotates in a twin-section housing. The section which carries the spindle is connected to the other section by a bayonet mount. The patent proposes to provide centering surfaces at both axial ends of the bayonet mount in order to reduce the likelihood of bending of the spindle when the holder is in use in a machine tool. The bayonet mount must be engaged and disengaged by hand. In addition, the bayonet mount cannot compensate for manufacturing and/or other tolerances, and the patented holder is effective only when the RPM of the spindle is below a certain value.